5:15 PM - 6:45 PM
[PPS04-P11] Dynamical and thermodynamical structure in cloud layer simulated by a GCM with correlated-k distribution radiative transfer model
★Invited Papers
Keywords:radiation, streak structure, meridional circulation, Venus
Recently, a more reliable general circulation in the Venus atmosphere has been depicted by the general circulation model "AFES-Venus" (Sugimoto et al. 2017) assimilated with the observation data acquired by the Venus Climate Orbiter AKATSUKI (Fujisawa et al., 2022) using "ALEDAS-V" (Sugimoto et al., 2017).
However, in earlier works using AFES-Venus, the radiative process, which is critical to simulate the thermodynamical structure of the Venus atmosphere, has been simplified by using prescribed solar heating and Newtonian cooling.
On the other hand, some groups have succeeded in developing sophisticated radiative transfer models and have used them in simulate general circulation models (e.g., Lebonnois et al., 2010; Yamamoto et al., 2019).
To extract more information and obtain more physically consistent inference from AKATSUKI, we should assimilate the model with not just retrieved but also directly observed variables such as cloud opacity and radiance (or another variable with a similar pattern).
To achieve this goal, we have incorporated a correlated-k distribution radiative transfer model for planetary atmospheres (Takahashi et al., 2023) into AFES-Venus.
In this presentation, we will report the dynamical and thermodynamical structure obtained by AFES-Venus with the radiative transfer model and compare the results with those obtained by previous AFES-Venus with prescribed solar heating and Newtonian cooling.
The numerical model used in this study is based on AFES-Venus, a modified version of AFES (e.g., Ohfuchi et al., 2005) to simulate the Venus atmosphere.
The added components in this study are a radiative transfer model and a surface process model to solve the planetary energy balance.
A primary limitation of our numerical model is an assumption of an ideal gas with a constant specific heat at constant pressure (Cp=900 J/(kg K); 1000 J/(kg K) in the previous studies).
In addition, prescribed radiatively active gas and cloud distribution (Crisp, 1986; Pollack et al., 1993) do not change with time and are horizontally uniform at an isobaric coordinate.
Time integration was performed until a statistical equilibrium was achieved (600 Earth years).
Here, we tuned the value of Cp to ensure that the static stability at a lower atmosphere (below 40 km height) becomes similar values to the observed one, and to mimic the observed Cp in the cloud layer.
After reaching the statistical equilibrium, the mean meridional circulation has three-cell like structures in vertical: the boundary layer, the layers around 20–30km, and the cloud layer above 50km.
Although the global mean temperature has a cold bias of up to 25 K from VIRA (Seiff et al., 1985), characteristics of the static stability and the latitudinal temperature gradient are qualitatively consistent with those observed.
Zonal winds in all layers below 90 km height are super-rotating with realistic intensity up to 100–130 m/s.
Circulations in the cloud layers are enhanced compared with the previous simplified model.
Similar to the observed radiance and high-resolution numerical study (Kashimura et al., 2019) by simplified model, the streak pattern is reproduced in our low-resolution simulation.
The low-stability layers localized in the polar region extend to the equatorial region, generating strong convections at the equator.
However, in earlier works using AFES-Venus, the radiative process, which is critical to simulate the thermodynamical structure of the Venus atmosphere, has been simplified by using prescribed solar heating and Newtonian cooling.
On the other hand, some groups have succeeded in developing sophisticated radiative transfer models and have used them in simulate general circulation models (e.g., Lebonnois et al., 2010; Yamamoto et al., 2019).
To extract more information and obtain more physically consistent inference from AKATSUKI, we should assimilate the model with not just retrieved but also directly observed variables such as cloud opacity and radiance (or another variable with a similar pattern).
To achieve this goal, we have incorporated a correlated-k distribution radiative transfer model for planetary atmospheres (Takahashi et al., 2023) into AFES-Venus.
In this presentation, we will report the dynamical and thermodynamical structure obtained by AFES-Venus with the radiative transfer model and compare the results with those obtained by previous AFES-Venus with prescribed solar heating and Newtonian cooling.
The numerical model used in this study is based on AFES-Venus, a modified version of AFES (e.g., Ohfuchi et al., 2005) to simulate the Venus atmosphere.
The added components in this study are a radiative transfer model and a surface process model to solve the planetary energy balance.
A primary limitation of our numerical model is an assumption of an ideal gas with a constant specific heat at constant pressure (Cp=900 J/(kg K); 1000 J/(kg K) in the previous studies).
In addition, prescribed radiatively active gas and cloud distribution (Crisp, 1986; Pollack et al., 1993) do not change with time and are horizontally uniform at an isobaric coordinate.
Time integration was performed until a statistical equilibrium was achieved (600 Earth years).
Here, we tuned the value of Cp to ensure that the static stability at a lower atmosphere (below 40 km height) becomes similar values to the observed one, and to mimic the observed Cp in the cloud layer.
After reaching the statistical equilibrium, the mean meridional circulation has three-cell like structures in vertical: the boundary layer, the layers around 20–30km, and the cloud layer above 50km.
Although the global mean temperature has a cold bias of up to 25 K from VIRA (Seiff et al., 1985), characteristics of the static stability and the latitudinal temperature gradient are qualitatively consistent with those observed.
Zonal winds in all layers below 90 km height are super-rotating with realistic intensity up to 100–130 m/s.
Circulations in the cloud layers are enhanced compared with the previous simplified model.
Similar to the observed radiance and high-resolution numerical study (Kashimura et al., 2019) by simplified model, the streak pattern is reproduced in our low-resolution simulation.
The low-stability layers localized in the polar region extend to the equatorial region, generating strong convections at the equator.